The continuous casting of molten metal into strips, sheets and slabs has been achieved through processes known as block casting. The term "metal" as used herein, refers to castable metal, including without limitation, aluminum, iron, steel, copper, zinc, manganese, magnesium, nickel and their alloys. Continuous block casters are particularly useful in the production of metal strip. Use of continuous block casters obviates the need to cast large ingots which must be repeatedly hot and cold rolled in order to obtain the desired thickness and microstructure of the cast. Moreover, it is easier to control the width of the strip being cast using continuous block casting methods than when using other processes to produce metal strip.
In a block, casting process, metal is supplied from a tundish to a continuously moving mold assembly consisting of two endless, counter-rotating beam chains. An endless beam chain is comprised of, among other things, several "blocks" which have been linked together to form a casting loop, giving the chain assembly a caterpillar track appearance. The beam chains are disposed in close relation to one another and travel in synchronized fashion in the casting direction. The mold cavity can further be defined by a side dam system to prevent movement of the molten metal in a direction transverse to the casting direction. In other embodiments, the blocks themselves can contain features, such as sidewalls, which prevent escape of the molten metal. As the molten metal contacts the moving mold, heat transfer occurs between the blocks, the side dams (if any) and the molten metal, resulting in solidification of the molten metal.
In nearly all block casters, the blocks are attached to "support beam" structures. This structure assists in preventing heat transmission from the blocks and thermal deformations of the blocks from affecting the performance of other caster assemblies requiring relatively small operating tolerances, such as the guideway track and the drive system. For example, U.S. Pat. No. 3,570,586, by Lauener, assigned to Lauener Engineering Ltd., discloses a caterpillar mold-type casting apparatus for casting metal strips which uses bolts as a block fastening apparatus to preclude heat transfer by conductivity from the chilling blocks to the caster guideway and drive.
The blocks in a continuous caster also require periodic replacement due to wear on their casting surfaces. Moreover, the blocks experience wear from the thermal and physical stresses experienced in moving through the casting loop. This can result in cracked or deformed blocks, causing a reduction in the quality of the cast. In order to replace individual blocks in the beam chain, the continuous casting operation must be halted. The continual stopping of a continuous caster for replacement of blocks leads to undesirable down-time and a decrease in production. For example, in a typical block caster containing sixty-four blocks, all sixty-four blocks may need to be replaced in a four-to-six week period of continuous operation. It is therefore desirable that replacement of blocks in a continuous caster be accomplished quickly.
Apparatus which use bolts for block fixation typically do not allow for rapid replacement of individual blocks. Alternatively, U.S. Pat. No. 4,784,210 by Takahashi et al., assigned to Ishikawajima-Harima Jukogyo Kabushiki Kaisha and Nippon Kokan Kabushiki Kaisha, discloses a method for installing and replacing blocks in a continuous block caster. The apparatus disclosed by Takahashi et al. consists of a plurality of clamps connected to the carriers which clamp directly onto steps located on the sides of the blocks. Takahashi et al. also disclose that the clamps on either sides of the block are connected to biasing springs and can be retracted to remove the block from the track by using piston rods located on both sides of the block. The method disclosed by Takahashi et al. however, uses a substantial number of moving parts and does not allow single point operation for simultaneously releasing a plurality of block fixation devices. Moreover, the clamps used by Takahashi et al. directly contact the block, and after thermal loading of the block can lead to undesirable deformation of the block or the supporting structure.
In addition to block fixation methods and apparatus, it is also desirable to control the positioning of the individual blocks in the beam chain. The positioning required for the individual blocks can depend, among other things, upon the casting application. In general, however, the casting surfaces of each block, and between blocks in the casting region should approximate a flat plane. Thermal and mechanical deformations, however, can occur as the blocks travel through the casting loop. Moreover, for some applications blocks cannot be produced economically to the tolerances required for use in a caster. For these reasons, it is desirable that the positioning of individual blocks be adjustable.
There are essentially three types of adjustments that can be made to the block position in a continuous caster. It is desirable that the individual blocks be capable of being adjustable in the casting direction (the "x-direction"), in the direction transverse to the casting direction (the "y-direction"), and in the direction normal to the casting direction, (the "z-direction"). These adjustments assist in preventing undesirable gaps and "steps" between blocks in the casting region, which reduce the quality of the cast and can cause damage to the caster. The adjustments also assist in preventing premature block wear by preventing unnecessary contact between adjacent blocks as they travel through the casting region.
Known methods and apparatus for fixation and adjustment of blocks in a continuous caster have met with limited success for the rapid replacement of blocks. Typical methods for block adjustment can be unstable and unreliable, can require high adjustment forces, and cannot be performed with high precision. Thus, it is desirable to provide an adjustment method and apparatus which has positive control, is reliable and reproducible.
It is desirable that adjustments to the blocks can be performed quickly and with precision, using minimal adjustment forces. The adjustments should also be reliable and stable enough not to vary over long term operation of the caster. Movement of the blocks during casting can result in blocks unnecessarily contacting adjacent blocks. Moreover, the adjustments should prevent variation during casting in the block-to-block step between blocks, known as "block level drift." Block level drift during casting can result in the formation of insulating gas pockets, causing poor heat transfer between the block surfaces and the metal being cast.